US 2009/0198094 A1 discloses an apparatus for determining a distribution of a selected therapy in a target volume. The apparatus comprises a three-dimensional ultrasound transducer for capturing volume data from the target volume and a computing device in communication with the three-dimensional ultrasound transducer for receiving the volume data. The computing device is further adapted to determine the distribution of the selected therapy in the target volume along a set of planned needle trajectories using the volume data, wherein at least one of the needle trajectories is oblique to at least one other of the planned needle trajectories. The quality of the ultrasound imaging may be reduced, which in turn may lead to a reduced accuracy of the determination of the distribution of the selected therapy in the target volume. If a brachytherapy is based on this determined distribution having a reduced accuracy, also the quality of the brachytherapy is reduced.